1. Technical Field
The present invention relates generally to the field of solar collectors having a parabolic trough to collect and concentrate the solar energy. The invention pertains more specifically to an extremely lightweight and low cost parabolic trough solar collector.
2. Background Art
Parabolic trough technology is currently the most advanced solar thermal electric generating technology. This is primarily due to nine large commercial-scale solar power plants, the first of which has been operating in the California Mojave Desert since 1984. These plants, which continue to operate on a daily basis, range in size from 14 to 80 MW and represent a total of 354 MW of installed electric generating capacity. Large fields of parabolic trough collectors supply the thermal energy used to produce steam for a Rankine steam turbine/generator cycle.
The collector field consists of a large field of single-axis tracking parabolic  trough solar collectors. The solar field is modular in nature and is composed of many parallel rows of solar collectors aligned on a north-south horizontal axis. Each solar collector has a linear parabolic-shaped reflector that concentrates the sun's direct beam radiation on a linear receiver located at the focus of the parabola. The collectors track the sun from east to west during the day to ensure that the sun is continuously focused on the linear receiver. A heat transfer fluid (HTF) is heated as it circulates through the receiver and returns to a series of heat exchangers in the power block where the fluid is used to generate high-pressure superheated steam. The superheated steam is then fed to a conventional reheat steam turbine/generator to produce electricity. Other solar concentrators convert the energy at the receiver directly into electricity via photovoltaic cells. There are unlimited uses of the energy concentrated on the receiver.
Exploitation of radiant solar energy is limited by the cost of the collection and conversion apparatus. To harvest substantial quantities of radiant solar energy requires substantial collection area which typically translates to substantial cost for both the collection and conversion apparatus. Reducing the cost of large area collectors motivates this invention.
The following issued U.S. Patents appear to constitute relevant prior art:
U.S. PAT. NO.PATENT DATEINVENTOR4,173,397Nov. 6, 1979Simpson4,432,342Feb. 21, 1984Lucas4,051,834Oct. 4, 1977Fletcher4,318,394Mar. 9, 1982Alexander4,071,017Jan. 31, 1978Russell4,920,033Apr. 11, 1989Sick4,243,019Jan. 6, 1981Severson4,454,371Jun. 12, 1984Folino4,077,392Mar. 7, 1978Garner4,515,148May 7, 1985Boy-Marcotte4,359,041Nov. 16, 1982Snodgrass4,293,192Oct. 6, 1981Bronstein4,291,677Sep. 29, 1981Monk
Of the foregoing prior art patents, the patents to Russell (U.S. Pat. No. 4,071,017) and to Simpson (U.S. Pat. No. 4,137,397) appear to be the most relevant.
Russell discloses a tensioned reflector support structure in which individual reflector planar slats are made independently moveable to focus reflected sunlight on a common receiver. The relevance results from the structure of each slat which employs tensioned cable pairs and a thin reflective sheet to form each slat mirror.
Simpson discloses a parabolic reflector sheet that is placed in tension against a plurality of tensioned wires to form the parabolic shape. Support bars are used to force the reflector against the wires.
Neither of these patents discloses use of a single, slidable, untensioned sheet reflector supported by pairs of fibers in contact with opposing surfaces of the sheet. Neither such patent discloses a transparent tubular enclosure that is pressurized to generate the tension in the fibers. Neither discloses a structure which is of comparable light weight or low cost.